This invention relates to a wireless device for high power transmission radio signal, which is for use in a TDMA (time division multiple access) system and a diversity reception system. Herein, it is to be noted that the wireless device can prevent any deterioration of local oscillator characteristics or transmission characteristics, and more prevent any breakage of parts such as transistors, filters or the like of receiver, due to occurrence of high power transmission radio signals.
Conventionally, the wireless device for use in the TDMA system is liable to undesirably cross or turn transmission signals from a transmitting portion into a receiving portion and into even a local oscillator through an antenna common switch, which is used in common to both reception and transmission signal paths. Such crossed transmission signals will be called cross components. In most of such the wireless devices, the high power transmission signal deteriorates not only local oscillator characteristics due to the cross components but also transmission characteristics. Furthermore, it often happens that a high power level of transmission signal breaks transistors, filters and the like which construct the receiving portion due to the cross components of the high power transmission radio signals.
In order to remove an interference of such cross components or interference, the wireless device has a BPF (band pass filter) which allows only the receiving signal frequency to pass therethrough. With this structure, the BPF can attenuate the transmission signal with a high level and then prevent the cross components of the transmission signal.
Another wireless device has been described in a Japanese Unexamined Patent Publication No. Hei 6-6275, namely, 6275/1994. The wireless device described in this publication can prevent such the transmission signal from being crossed into the receiving portion.
Referring to FIG. 1, the wireless device comprises a plurality of antennas 101 and 101N, a plurality of antenna common switches 102 and 102N, a receiving portion, a transmitting portion and a switch controller 111. Each of the antenna common switches 102 and 102N switches connections between the antenna 101 or 101N and the receiving portion and between the antenna 101 or 101N and a hybrid 110 of the transmitting portion for radio signals from one to another. The receiving portion performs a reception diversity for the antennas 101 and 101N, while the transmitting portion performs a transmission diversity by the use of the antenna 101 or 101N selected by the reception diversity.
The receiving portion comprises RF/IF (radio frequency/intermediate frequency) receivers 103 and 103N, demodulators 104 and 104N, a level comparator 105, and a selector 106. The RF/IF receiver 103 and the demodulator 104 are provided for each of the antenna common switches 102 and 102N. The level comparator 105 compares signal levels measured by the demodulators 104 and 104N with each other and decides one of the RF/IF receivers 103 and 103N by reception diversity. And the selector 106 selects one of the outputs sent from the demodulators 104 and 104N in accordance with the information from the level comparator 105.
On the other hand, the transmission portion comprises a burst generator 107, a modulator 108, and an IF/RF transmitter 109. The burst generator 107 produces burst signals from carrier signals. The modulator 108 modulates the burst signals by the IF (intermediate frequency). The IF/RF transmitter 109 converts the IF modulated signals into the RF (radio frequency) which is send to a hybrid 110 as radio signals.
The hybrid 110 distributes the RF signals or the radio signals to all of the antennas 101 and 101N, respectively. The switch controller 111 controls the antenna common switches 102 and 102N each of which connects between the antenna 101 or 101N and each reception portion correspondingly for the reception diversity. Then, by the switch controller 111, the antenna common switch 102 or 102N connects the RF/IF receiver 103 or 103N with an antenna 101 or 101N selected by the information from the level comparator 105, under control of the switch controller 111 when the radio signal is received. On transmission, the switch controller 111 controls the antenna common switch 102 or 102N to connect the transmission portion to the same antenna 101 or 101N used in the reception of the radio signal. Thus, the diversity transmission is carried out.
The local oscillator 112 generates local oscillation signals for use in frequency conversion of signals supplied to the RF/IF receivers 103 and the IF/RF transmitter 109. However, in the above-described publication, an oscillator switch 113 is located between the local oscillator 112 and the IF/RF transmitter 109. As a result, the local oscillator 112 is connected with the IF/RF transmitter 109 only on the transmission of radio signals to the antenna 101 or 101N.
In the case where the radio signal is transmitted by the use of the above-described construction, the local oscillation signals are given from the local oscillator 112 to the transmitting portion, and are rendered into the transmission radio signals which are sent out from the antenna 101 or 101N selected by the reception diversity.
On the other hand, during the signal reception, the transmission of the radio signals from the transmitting portion to the antenna, is stopped. Accordingly, during the reception of the radio signals, even if isolation among the antennas, the receiving portion, and the transmitting portion is not sufficient, it is possible to protect the transmission radio signals from being crossed into the signal reception side. And with this structure, good diversity can be accomplished on signal reception.
However, during the transmission of the radio signal, it is difficult to prevent the transmission radio signal from being crossed into the receiving portion, if the isolation is insufficient.
In the wireless device described above, the high power transmission radio signal is inevitably given to the local oscillator through the signal receiving portion. Therefore, the BPF is provided for attenuating the transmission signal within the predetermined frequency band. However, such a BPF is difficult to be designed and complicated in structure. Accordingly, the wireless device is complicated in structure and expensive.